The following message was observed in a customer log:
2021-05-12 04:54:02,043+0000 WARN [qtp976626720-3335210] *UNKNOWN org.sonatype.nexus.repository.pypi.internal.orient.OrientPyPiProxyFacetImpl - An error occurred re-writing the index for package example
The actual error was not logged, only that there was one. Further there was no corresponding request.log line with the same thread id to match to error, so we can't even tell what the client may have seen here.
If you are logging a WARN message about a problem, always log some context, what happened, what type of error, while processing what thing - As much as possible. Always propagate any such error to the request.log line if driven by an actual request thread.